Integrated Laser Alignment Aid Using Multiple Laser Spots Out Of One Single Laser

ABSTRACT

The present invention relates to light curtains, in particular safety light curtains, for monitoring a protective field. Furthermore, the present invention relates to optical units which are part of such a light curtain. An optical unit for an alignment system of a light curtain monitoring a protective field comprises an optical processing element for generating a defined radiation pattern from the radiation emitted by an alignment radiation source, and at least one additional optical functional element being formed integrally with the optical processing element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.13/757,321 filed on Feb. 1, 2013, which claims priority to EuropeanApplication No. EP12153555 filed on Feb. 2, 2012, the disclosures ofwhich are expressly incorporated herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH BACKGROUND OF THEINVENTION

The present invention relates to light curtains, in particular, safetylight curtains for monitoring a protective field. Furthermore, thepresent invention relates to optical units which are part of such alight curtain.

Generally, light curtains detect the movement or intrusion of objectsinto guarded zones, and more particularly, provide protection for humanoperators who are working with machines or other industrial equipment.

Light curtains employing infrared or visible light beams are used toprovide operator safety in a variety of industrial applications. Lightcurtains typically are employed for operator protection aroundmachinery, such as punch presses, brakes, molding machines, automaticassembly equipment, coil winding machinery, robot operation, castingoperations and the like. Conventional light curtains typically employlight emitting diodes (LED) mounted at spaced positions along atransmitter bar at one side of the guard zone and phototransistors (PT),photodiodes or photoreceivers mounted along a receiver bar at theopposite side of the zone. The LEDs transmit modulated infrared lightbeams along separate parallel channels to the PTs at the receiver bar.If one or more beams are blocked from penetration by an opaque object,such as the operator's arm, a control circuit shuts the machine down,prevents the machine from cycling, or otherwise safeguards the area.

Usually, safety light curtains comprise two optical units (called bars,sticks, or strips), which are formed as two different constructionalunits, one of the optical units having the functionality of an emitterand one of a receiver. This dedicated architecture of an emitter andreceiver, however, has several drawbacks, for instance the fact that thefabrication costs are high, because each type of optical unit has to befabricated differently. Consequently, there exist concepts that use anarchitecture wherein each optical unit has a transceiver unit carrying aplurality of light emitting elements and light receiving elements and atleast one separate detachable plug-in module. The first and secondtransceiver units are identically built, whereas the first and secondplug-in modules differ from each other and thus define the functionalityof the respective optical unit. For instance, the plug-in moduledifferentiates an optical unit as the emitter with, for instance, thetest input, or as the receiver with, for instance, the output signalswitching devices, OSSD.

Such a modular architecture is for instance proposed in the Europeanpatent application EP 11162263.5 and allows a very cost-effectivefabrication, because the transceiver modules are identically built and,furthermore, can be applied in a very flexible way for a multitude ofapplications and system configurations.

However, this modular transceiver bar configuration is not compatiblewith laser alignment techniques that employ one laser module as aradiation emitter at each stick, but at different locations for thededicated receiver and transmitter bar, respectively, as this is forinstance shown in the published European patent EP 0889332 B1.

In order to provide an alignment system for systems based on transceiverbars according to the European patent application EP 11162263.5, onepossible solution could therefore be seen in providing two laser modulesfor each transceiver bar. This concept, however, increases the costs dueto the additional laser emitter for each transceiver bar.

The object underlying the present invention is to provide a lightcurtain and an optical unit for a light curtain, which can be fabricatedin a particularly cost-effective way, and allow for an accuratealignment and synchronization.

This object is solved by the subject matter of the independent claims.Advantageous embodiments of the present invention are the subject matterof the dependent claims.

SUMMARY OF THE INVENTION

The present invention is based on the idea that one laser module in eachstick can be employed when using an optical processing element thatgenerates a defined radiation pattern, for instance a row of multiplespots along the axis of the sticks and a target where the spotsgenerated by the opposing laser module are clearly visible ordetectable. With such a configuration, both sticks are still identicaland no supplementary laser modules are necessary for providing anaccurate alignment.

In particular, an alignment system for a light curtain monitoring aprotective field comprises at least one alignment radiation source beingarranged on a first support element of the light curtain and at leastone alignment radiation receiver arranged on the second support element.This alignment radiation receiver provides an alignment signalindicating a correct positioning of the two support elements withrespect to each other.

According to the present invention, the alignment system has at leastone optical unit which has an optical processing element for generatinga defined pattern from the radiation emitted by the alignment radiationsource. This defined pattern can be detected by the alignment radiationreceiver and the alignment signal can be generated based on the incidentradiation.

The radiation receiver may be just a target surface where the radiationpattern emitted by the opposing laser module is clearly visible and canbe evaluated by an operator adjusting the position of the light curtainsystem. However, also more sophisticated sensor systems can be used forevaluating the position of the opposing stick. According to the presentinvention, the optical processing element is structured to form in aplanar observation region, a plurality of light points arranged in anessentially straight line from the radiation of the laser radiationsource. By splitting one laser spot into various spots an alignmentaccuracy can be reached which normally is only achieved by using morethan one laser radiation sources.

A particularly cost effective and on the other hand precisely alignedmounting of the optical unit according to the present invention can beachieved by combining the optical processing element which generates thedefined radiation pattern, with at least one additional functionalelement, such as a lens for focussing the light curtain radiation,and/or an optical waveguide that is needed for guiding the radiationfrom at least one display radiation source to a surface which is visibleto an observer and/or a beam expander. Such a combined optical unit hasa size sufficiently large for a facilitated assembly and may even haveadditional alignment features for being mounted within the housing of asupport element, but on the other hand only needs a relatively smallpart forming the optical processing element. The optical unit may forinstance be fabricated as a molded part from a plastic material or as amicromachined part made from glass, quartz, or plastic. The actualoptical processing element may be fabricated from the same material orfrom a different material as the optical unit.

In case that the optical unit also incorporates a lens arrangement, inan advantageous way two low tolerance fabrication processes canefficiently be combined because the lenses also have to be fabricatedand mounted with particularly high accuracy.

Because the optical processing element is incorporated into the opticalunit in the frame of a high-precision fabrication step as it iswell-established in micro machining technology, its position with regardto the optical waveguides or any other alignment features can beperformed accurately and with small tolerances. The position of theoptical unit with regard to the support element of the light curtain, onthe other hand, is facilitated because the optical unit is large enoughto be mounted in a particularly easy way.

According to the present invention, the optical processing elementcomprises a micro-structured Diffractive Optical Element (DOE), anoptical grating structure and/or a prismatic structure for generating adefined pattern from the radiation emitted by the alignment radiationsource.

DOEs utilize surfaces with a complex micro structure for a particularoptical function. A micro-structured surface relief profile has two ormore surface levels. The surface structures are for instance etched infused silica or other glass types, or are embossed in various polymermaterials. As this is generally known, Diffractive Optical Elements workby breaking up incoming waves of light into a large number of waveswhich re-combine to form completely new waves. They can be fabricated ina wide range of materials, such as aluminium, silicon, silica, plasticsetc., providing the user with high flexibility and selecting thematerial for a particular application.

According to the present invention, a micro-structured DOE is used forgenerating a defined pattern of light from one single radiation source.

According to an advantageous embodiment, a plurality of light points isgenerated which are arranged in an essentially straight line. Thestraight line of light points can be used for evaluating whether thelight curtain support elements are correctly aligned with respect toeach other.

However, also any other shape of radiation pattern may be used forperforming the alignment. For instance, also concentric circles orparallel lines may be generated from one radiation source.

According to the present invention, the light points have differentintensity, the central point having a higher intensity compared to theremaining points for facilitating horizontal and vertical alignment ofthe support elements. However, uniform intensity can also be chosen.

Although DOEs have several significant advantages over conventionalrefractive optical elements, gratings or prismatic structures may ofcourse also be used in the optical unit according to the presentinvention.

According to the present invention, the additional optical functionalelement may also comprise a beam expansion unit for adapting a crosssectional shape of a beam emitted by the alignment radiation source tothe dimension of an active area of the optical processing element. Inparticular, when using a prismatic structure in the optical processingelement, a certain size of the optical processing element cannot beundercut. Consequently, a certain minimal radiation beam diameter isrequired to illuminate all parts of the structure. Therefore, accordingto an advantageous embodiment of the present invention, a beam expansionunit is integrated in the optical unit so that the radiation beam, inmost cases a laser beam, has a sufficiently large diameter. As a beamexpansion unit, firstly, well-established techniques for providing laserexpanders can be exploited.

For instance, a lens system according to a Kepler or a Galileo beamexpander configuration can be integrated into the optical unit. As thisis generally known, in general laser applications, two basic ways ofimplementing beam expansion systems are known, firstly the Keplerarrangement consisting of two positive lenses or groups of lenses, andsecondly, the Galileo configuration consisting of a negative and apositive subsystem. Due to the reduced installation length, the Galileoarrangement will, in most cases, be preferred for the present invention.

Furthermore, also a cylindrical lens structure preferably formed as oneintegral part from glass or plastic material can be used as a beamexpansion unit. The advantage of such a beam expansion unit can be seenin a particularly easy fabrication and a space-saving shape.

As an alternative to the lens-based beam expansion unit, also abirefringent element can be used for expanding the radiation beam to belarge enough for interacting with the complete optical processingelement area. The advantage of using a birefringent material can be seenin the fact, that a beam expander unit based thereon is much easier tobe fabricated than a double lens system.

In order to enhance the accuracy of the alignment of the optical axis ofthe alignment radiation source, the optical unit itself may comprise ameans for aligning the position of the laser with respect to the opticalunit and thus to the optical processing element. These alignment meansmay be formed, for instance, by a recess that interacts with passing ofthe alignment radiation source for accurately positioning same with inthe optical unit. For instance, an alignment shoulder or one or morealignment ribs can be provided in this recess. Providing a shoulderwhich extends across to the longitudinal axis of the alignment radiationsource has the advantage that a much higher accuracy can be achieved.

According to the present invention, the optical processing elementcomprises a prismatic structure having a plurality of angled surfacesand a uniform base surface opposite to these angle surfaces. Such astructure may easily be produced and has the advantage of generating thedesired radiation pattern in a very flexible and accurate way. Inparticular, by using different sizes of the particular prismatic areas,spots of differing brightness can be generated. The plurality ofdifferent prisms are all fabricated with one molding tool, if a moldingtechnique is used. By partitioning the tool correspondingly, sharp edgescan be achieved for the prismatic structure. Furthermore, by providingthe base surface with an orientation regarding the optical axis of theincident alignment radiation beam so that it includes an angle differentfrom 90° with the optical axis, the overall thickness of the opticalprocessing element can be kept much more uniform, thus facilitating themolding process.

According to the present invention, a light curtain for monitoring aprotective field comprises a first support element and a second supportelement, wherein the protective field is covered by radiationtransmitted between these support elements and an alignment systemaccording to the present invention. By designing each support elementessentially identical and distinguishing between the function of thesupport elements only via different plug-in elements as this is knownfrom EP 11162263.5, a particularly cost-effective fabrication of thelight curtain can be achieved. For performing the alignment, an operatormay either evaluate the alignment radiation pattern on a particularsurface of the opposing support element, or optoelectronic detectors maybe provided for measuring the incident radiation pattern and forgenerating an electrically processible output signal.

These and other objects, advantages and aspects of the invention willbecome apparent from the following description. The particular objectsand advantages described herein may apply to only some embodimentsfalling within the claims and thus do not define the scope of theinvention. In the description, reference is made to the accompanyingdrawings which form a part hereof, and in which there is shown apreferred embodiment of the invention. Such embodiment does notnecessarily represent the full scope of the invention and reference ismade, therefore, to the claims herein for interpreting the scope of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of an optical unit according to a firstadvantageous embodiment;

FIG. 2 shows a side view of the optical unit of FIG. 1;

FIG. 3 shows another side view of the optical unit of FIG. 1;

FIG. 4 shows a top view of the optical unit according to FIG. 1;

FIG. 5 shows a sectional view of the optical unit according to FIG: 1;

FIG. 6 shows another sectional view of the optical unit according toFIG. 1;

FIG. 7 shows an example of a radiation pattern generated by the opticalprocessing element according to the present invention;

FIG. 8 shows an alignment of two short support elements with respect toeach other;

FIG. 9 shows the alignment of two longer support elements;

FIG. 10 illustrates the allowable rotation for the short light curtainsupport element;

FIG. 11 shows the allowable rotation for longer light curtains;

FIG. 12 illustrates a part of a phase grating of a DOE;

FIG. 13 shows the distribution of light in the far field for the gratingof FIG. 12;

FIG. 14 shows a periodic grating;

FIG. 15 shows the energy distribution in the far field generated by thegrating of FIG. 14;

FIG. 16 shows a prismatic structure;

FIG. 17 shows the light distribution generated by the prismaticstructure of FIG. 16;

FIG. 18 shows the housing of a support element according to the presentinvention;

FIG. 19 shows a perspective view of an optical unit according to asecond advantageous embodiment;

FIG. 20 shows a side view of the optical unit of FIG. 19;

FIG. 21 shows a sectional view of the optical unit according to FIG. 19

FIG. 22 shows a top view of the optical unit according to FIG. 19;

FIG. 23 shows another sectional view of the optical unit according toFIG. 19;

FIG. 24 shows another sectional view of the optical unit of FIG. 19;

FIG. 25 shows a schematic representation of an intermediate laser beamshaping unit based on a cylindrical lens structure;

FIG. 26 shows a schematic representation of an intermediate laser beamshaping unit based on a birefringence material;

FIG. 27 shows a perspective view of a laser radiation emitting unitaccording to a first advantageous embodiment;

FIG. 28 shows a cut view of the laser radiation emitting deviceaccording to FIG. 27 when mounted in an optical unit according to thepresent invention;

FIG. 29 shows a perspective view of a laser radiation emitting unitaccording to a second advantageous embodiment;

FIG. 30 shows a cut view of the laser radiation emitting deviceaccording to FIG. 29 when mounted in an optical unit according to thepresent invention;

FIG. 31 shows a schematic cross-sectional view of a further prismaticstructure to explain its fabrication;

FIG. 32 shows a schematic cross-section of the prismatic structure ofFIG. 16;

FIG. 33 shows a schematic cross-section of a prismatic structure with amore uniform thickness.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, an optical unit according to the presentinvention is explained in more detail.

The optical unit 100 is designed to be mounted within a support elementof a light curtain monitoring a protective field. The optical unit 100is combining several optical functions as one integral part: Firstly, itaccommodates an optical processing element 102 for generating a definedradiation pattern from the radiation which is emitted by an alignmentradiation source (not shown in the figure). The optical processingelement 102 may for instance comprise a micro-structured DiffractiveOptical Element (DOE) which transforms the radiation emitted by aradiation source, such as a laser diode, into a pattern that can be usedadvantageously for aligning a support element to which the optical unit100 is connected with respect to a second support element of a lightcurtain arranged in some distance thereto.

For a person skilled in the art, it is however clear that the opticalunit 100 according to the present invention may advantageously be usedalso for other alignment tasks which utilize optical radiation for theactual alignment.

The optical processing element 102 may form a row of light dots, anarray of light dots, a plurality of lines, concentric circles or squarestructures or any other suitable form from the incident laser beam whichcan be used for an alignment. In the following, only the example offorming a plurality of light points which are aligned in a straightline, will be explained in more detail, because such a linear pattern isan advantageous means for detecting a misalignment of two light curtainsupport elements with respect to each other.

According to the present invention, the optical processing element 102is embedded integrally within the main body 104 of the optical unit 100.Such a construction can either be achieved by forming the opticalprocessing element 102 directly from the same material as the main body104 or by separately manufacturing the optical processing element 102and—for instance—overmolding same when fabricating the main body 104.

According to the present invention, the optical unit 100 is producedfrom a plastic material, or from glass or quartz, either as a moldedpart or as a micro-machined part.

According to the present invention, as additional optical functionalelements, one or more optical waveguides 106 are integrally formed withthe main body 104. The optical waveguides 106 guide radiation from atleast one display radiation source (not shown in the figures) to asurface 108 of the optical element which is visible for an observer.Such a compact construction of the optical unit 100 allows for a muchmore precise alignment of the optical processing element 102 withrespect to a support element of a light curtain, because of the largersize and the oblong form. The position of the optically activestructures of the optical processing element 102 with respect to themain body 104 of the optical unit can be adjusted during ahigh-precision fabrication step when producing the optical unit 100,whereas the alignment of the optical unit 100 in a support element isdone by a mechanical fit, as this will be explained later with respectto FIG. 18.

Furthermore, the optical unit 100 additionally comprises an array oflenses 107 which will be mounted in a way that they focus incident lightcurtain radiation onto a receiver element and/or form an emittedradiation beam from an emitter element. In the present case, forinstance a row of 18 lenses is integrally formed with the opticalprocessing element 102 and the optical waveguides 106. For a personskilled in the art it is of course clear that also only a lens array(even differently shaped) without the waveguides 106, or any otherrequired optical functional elements may be combined with the opticalprocessing element 102 in order to enhance the mounting precision of theoptical processing element 102.

FIGS. 2 to 6 show several sectional and side views of the optical unit100 according to FIG. 1. Depending on the material from which theoptical processing element 102 is made, same can be fabricated directlyfrom the material from the main body 104 or can be incorporated forinstance by overmolding a pre-fabricated optical chip. As alreadymentioned above, the optical processing element 102 may comprise amicro-structured DOE. However, also a simpler optical grating structureor a prismatic refractive structure may be chosen for forming thedesired radiation pattern from the radiation emitted by an alignmentradiation source, such as a laser.

The optical waveguides 106 guide the light from corresponding lightsources, such as light-emitting diodes (LEDs) to the outer surface 108where the light is visible for an observer. Here, a slightly taperedform of the optical waveguides 106 was chosen in order to generate asufficiently large light point on the display surface 108.

FIG. 7 schematically illustrates the functioning of the opticalprocessing element 102 according to one particular example. It has to bementioned that the present drawing is not to scale, in order to enhancethe clarity for the following explanations.

An alignment radiation source 110, for instance a laser module with acollimator, generates a laser beam 112. The laser beam 112 passesthrough the optical processing element 102. In the present example, thisis a Diffractive Optical Element (DOE), which splits the laser beam 112into a plurality of beams forming a straight line of dots 114 on atarget surface 116. As already mentioned, also other radiation patterns114 than the one schematically shown in FIG. 7 can be achieved. In thepresent example the laser beam 112 is split into a radiation pattern 114having a centre spot with larger intensity and a plurality of smallerlight points with lower intensity. The distance between the opticalprocessing element 102 and the target surface 116 for the presentexample may, for instance, be up to 18 m. The maximum angle indicated inFIG. 7, α_(max), is around 4.25°, whereas the minimum angle between thecentral beam and the next following weaker beam, α_(min), amounts toabout 0.45°. For a correct alignment of one stick of a light curtain,where the laser module and DOE is mounted, with respect to a secondstick representing the target surface, about ten light spots are needed,so that the upper half of the beams above the central beam can be usedand the lower half of FIG. 7 would not be necessary.

According to the present invention, the optical unit 100 as shown inFIGS. 2 to 6 forms part of an alignment system that is used for aligningtwo sticks of a light curtain with respect to each other. FIG. 8 showsthe alignment of a first light curtain stick 118 and a second lightcurtain stick 120. In the example shown in FIG. 8, only the first lightcurtain stick 118 has a laser radiation emitting device and optical unitaccording to the present invention, whereas the second light curtainstick has the function of a target surface. However, for a personskilled in the art it is clear that of course also both light curtainsmay be equipped with an alignment radiation source.

Furthermore, even if it might be advantageous to use the combinedoptical unit 100 having waveguides and an optical processing element inan integrated form, the general idea of aligning light curtain stickswith respect to each other by employing an optical processing element102 can of course also be realized by only using a radiation source andthe optical processing element, as explained with respect to FIG. 7.

In FIG. 8 the alignment of two rather short light curtain sticks, forinstance having a length of about 150 mm, is explained. It is assumedthat the first light curtain stick has an alignment radiation source andoptical processing elements, which generate a radiation pattern 114, asshown in FIG. 7.

As can be seen from FIG. 8, in a distance of 2 m between both sticks andbelow, all ten light spots can be evaluated on the second light curtainstick 120. A distance of 6.8 m and 9.5 m are the limit for still beingable to use the third and second beam, respectively. The fact that atleast two light points, i.e. the central beam and the first side beamare needed for an alignment, leads to the limit of a distance of 19 musing the particular radiation pattern of FIG. 7 with a minimal angle αmin of 0.45° and a maximum angle of α max is 4.25°.

On the other hand, as shown in FIG. 9, with a radiation pattern 114 asshown in FIG. 7, all ten light spots are visible on a light curtainstick of 1.50 m in a distance from the light source of 20 m. Short lightcurtain systems, as the one depicted in FIG. 10, allow for an operationdistance between 10 m and 18 m and a maximum rotation of ±50° at adistance between 2.00 m and 2.15 m without interruption of the lightcurtain. In a distance range between 2.15 m and 20 m, a completerotation of the position between the two sticks is possible withoutinterrupting the light curtain.

The allowed rotation for long light curtain sticks is schematicallydepicted in FIG. 11. Depending on the operating distance between thefirst and second light curtain stick, and assuming an effective apertureangle of about 2°, the laser spot tolerances for correct operation aregiven on the right-hand side of FIG. 11, whereas the maximum possiblerotation angle is summarized on the left-hand part of FIG. 11. Themaximum possible rotation occurs at 18 m and amounts to ±45°.

In summary, the alignment system using a radiation pattern, as shown inFIG. 7, at a two metres distance and a length of the light curtainsticks of 1500 mm allows a rotation of 5° of the stick. With a 14 mmdeviation of the topmost laser point or a 131 mm deviation of thetopmost end of the stick, the line of light points can still easily beseen. Generally, it could be shown that longer sticks at short distancesare easier to align (refer to FIG. 9).

From a more abstract point of view, the optical processing unit 102should be designed in a way to generate a desired light pattern from agiven radiation beam. In the above-explained example, this should be forinstance a row of ten laser radiation points having a distance of about0.4°. As already mentioned, there exist several possibilities oftransforming the light from one radiation source into such a pattern.The first possibility is the use of a computer-generated DiffractiveOptical Element (DOE). FIG. 12 depicts an example of a phase grating ofsuch a DOE. Such a DOE has the advantage that the desired radiationpattern can be generated with the highest flexibility and accuracy.However, the fabrication expenditure is rather high and—as a binary DOEis not sufficient to generate this radiation pattern—a four-step DOE, asshown in FIG. 12, has to be designed.

FIG. 13 shows the light distribution, which is generated in the farfield. In particular, the squared amplitude is shown as a function ofthe position.

Alternatively, an optical grating of a periodic form can be used asshown in FIG. 14. This structure is also based on the principle of lightdiffraction, but is much easier to fabricate. However, a periodicdiffraction grating as shown in FIG. 14 has the disadvantage that thedegree of the energy distribution can be influenced to a much smallerextent. FIG. 15 shows the energy distribution in the far field, whichcan be generated by using the periodic grating of FIG. 14 for an opticalprocessing element 102 according to the present invention.

Finally, not only diffraction, but also refraction can be used forgenerating a radiation pattern suitable for an alignment of two lightcurtain sticks with respect to each other. FIG. 16 shows such aprismatic structure and FIG. 17 depict the belonging light distributionin a distance of 3 m. A linear structure of prisms with steadilychanging angles, as shown in FIG. 16, also has the advantage of thecomparatively simple fabrication. A disadvantage of using a prismaticstructure can be seen in the fact that the laser points are deformed bysome extent and that when using a small laser cross section, mountingtolerances have therefore to be taken into account.

FIG. 18 shows an example of a light curtain support element 122, whichon the one hand is formed to accommodate the optical elements forforming the light curtain and, on the other hand, has a recess 124 formounting the optical unit 100′ (as shown in the following FIGS. 19 to24) according to the present invention.

When using the present invention in the frame of a modular transceiverbar according to European patent application EP 11162263.5, both supportelements of the first and the second light curtain stick can be formedidentically, each having the recess 124. The functionality of therespective light curtain stick is then defined by a plug-in module (notshown in the figure). In this case, the alignment radiation source whichis housed in the opening 126, can either be left inactive for one of thelight curtain sticks or it can be used in both directions.

An alternative embodiment of an optical unit 100′ is shown in FIGS. 19to 24. The main difference to the first example is the omission of thelenses and the reduction of the material in the area of the main body104′. In contrast to the optical unit 100 shown in FIGS. 1 to 6, thisembodiment has longer optical waveguides 106′, and firstly allows afabrication which adds the optical waveguides from a different materialas the main body 104′ and furthermore, needs less material that might becostly, if it is for instance fused silica or another micro-machinedpart.

In summary, the present invention firstly has the advantage that byusing a Diffractive Optical Element (DOE) a laser beam is split intovarious spots of different intensity so that a central spot is easilyvisible, thus facilitating a horizontal alignment, whereas all othersare arranged in one exact row, thus facilitating the vertical alignment.This alignment system allows for a much cheaper alignment of the twosticks of a safety light curtain, because the building of two identicalsticks is possible and only one laser module for each stick is required.A direct comparison shows that even when using as the optical processingelement a computer-generated DOE, same is cheaper than providing anadditional laser module.

Furthermore, when combining the optical processing element with one ormore additional optical functional elements, such as lenses or opticalwaveguides to form optical units according to the present invention, anaccurate positioning of the element within the module is possible, thusproviding the spots in the required tolerance. The optical unit is alonger element than only a DOE chip, but is less costly than providing alarger DOE.

A further aspect of the present invention will now be explained withreference to FIGS. 25 and 26. For most of the optical processing units102 shown in the previous figures, a laser beam diameter is needed whichexceeds the dimensions that can be reached by conventional alignmentradiation sources 110. Consequently, for widening the laser beam, a beamexpanding unit 128 may be provided as shown in FIG. 25. The initiallaser beam 112 is expanded to an expanded laser beam 113 having anelliptical cross-section which is larger than the circular diameter ofthe initial laser beam 112.

It could be shown that by providing a laser beam with an elliptic orline shaped diameter which has a longitudinal axis that reaches bothends of the optical processing element, a sufficiently split radiationpattern can be generated. Such a widening of the circular beam isnecessary for a combination of the optical processing element 102 withstandard laser modules because for proper functioning of the opticalprocessing element, a sufficient number of the different structurespresent on the optical processing element 102 have to be illuminated.For instance, in the case of a prismatic structure, each of theindividual prisms has to be illuminated.

Downsizing the geometric dimensions of these prisms is normally not anoption because there are usually limits to their miniaturisation due tofabrication restrictions. However, it is not necessary to use a laserbeam with a circular cross-section; a widening to an ellipticcross-section is sufficient. The advantage of using standard lasermodules with small round beam diameters together with a beam expandingunit 128 can further be seen in the fact that the orientation of thelaser module 110 with respect to its rotational angle around the beamaxis does not have to be adjusted during assembly. The orientation ofthe elliptic cross-section of the laser beam arriving at the opticalprocessing element 102 is aligned by the orientation of the beamexpanding unit 128 which can be fabricated together with the opticalprocessing element allowing for low tolerances. The expanded laser beamgenerates a homogeneous illumination of all parts of the opticalprocessing element 102, thus ensuring proper generation of the radiationpattern.

For expanding the laser beam, all known expander principles may be used.For instance, a Kepler or Galileo arrangement in a miniaturisedmicrostructured form can be implemented.

The beam expanding unit 128 may also comprise a birefringent material,as shown in FIG. 26.

As this is generally known, crystals are classified as being eitherisotropic or anisotropic depending upon their optical behaviour.Anisotropic crystals have crystallographically distinct axes andinteract with light in a manner that is dependent upon the orientationof the crystalline lattice with respect to the incident light. Whenlight enters along the optical axis of an anisotropic crystal, it actsin a manner similar to the interaction with isotropic crystals andpasses through at one single velocity. However, when light enters alonga non-equivalent axis, it is refracted into two rays; each polarisedwith the vibration directions or vented at right-angles to one anotherand travelling at different velocities. This phenomenon is termed“double-” or “bi-refraction” and is seen to a greater or lesser degreein all anisotropic crystals. When anisotropic crystals refract light,the resulting rays are polarised and travel at different velocities. Theray which travels with the same velocity in every direction through thecrystal is termed the “ordinary ray” as shown in FIG. 26.

The other ray travels with a velocity that is dependent upon thepropagation direction within the crystal. This light ray is termed the“extraordinary ray”. The distance of separation between the ordinary andextraordinary ray increases with increasing crystal thickness 130. Inorder to ensure that there will be no gap between the ordinary beam andthe extraordinary beam, a well-defined maximum thickness of the beamexpanding unit 128 will have to be maintained. By appropriately choosingthe material, orientation and thickness of the birefringent beamexpanding unit 128, an enlarged diameter of the laser beam can beachieved by superposing the ordinary beam 132 and the extraordinary beam134.

Proper functioning of the optical axis of the radiation source 110 withrespect to the optical processing element 102 is important. Inparticular, the laser beam should have a well-defined angle of incidencewith respect to the surface of the optical processing element, usually90°. Due to the small dimensions of the radiation sources usable withthe present invention, alignment features should be provided at thesupport elements which hold the radiation source 110 and the opticalprocessing element 102.

An advantageous possibility of certain alignment will be explained withrespect to FIGS. 27 and 28. According to this embodiment, the lasermodule 110 has a cylindrical housing 136 with a circumferential stepformed shoulder 138. As can be seen from FIG. 28, the shoulder 138interacts with the stop 140 which is provided in a mounting recess 142of the optical unit 100. The stop 140 can be fabricated with highaccuracy in regard to the position of the optical processing element102. Consequently, the optical axis of the radiation source 110 can beefficiently aligned with the optical processing element 102. Thetolerances can be kept small because surfaces being perpendicular to theoptical axis act as a reference. By additionally providing potholes inthe recess in the optical unit 100, glue can be deposited which will fixthe laser module 110 in the optical unit 100 permanently.

A different shape of a laser module is shown in FIGS. 29 and 30.According to this embodiment, the radiation source 110′ has an elongatedcylindrical housing which does not have any protrusions thereon. In thiscase, as may be derived from FIG. 30, the outer longitudinal surface ofthe cylinder is used for aligning the optical axis of the laser module110′ with respect to the optical processing element 102. For thisalignment, the recess 142 wherein the laser module 110′ is mounted, hasprotruding guiding ribs for aligning and centring the laser module 110′.Again, glue can be used for fixing the laser module 110′ within therecess 142.

When additionally taking into account FIG. 18, it is clear for a personskilled in the art that the recess 142 of FIGS. 27 and 28 or 29 and 30,respectively, may also at least partly be formed in the light curtainsupport element 122 whereto the optical unit 100 is mounted.

With respect to FIGS. 16 and 17, a first advantageous prismaticstructure for implementing an optical processing element 102 accordingto the present invention has been explained. However, there are severalfurther possibilities of designing such a prismatic optical processingelement 102. A further advantageous embodiment is shown in FIG. 31. Theprism structure of FIG. 16 has a regular order of the prisms; each prismregion having the same width of 0.08 to 0.36 mm each, depending ontooling options and laser beam diameters. This structure has to berepeated at the borders because of the laser beam position tolerancesand the width of each prism should be adjusted to the individual beambrightness requirements.

Referring now to FIG. 31, the prismatic structure has a total width w ofless than 2 mm. In order to generate all split laser beams except thosewhich are redundant, the laser beam must have a minimum diameter ofabout two thirds of the total width.

FIG. 31 also schematically illustrates a fabrication tool for moldingthe optical processing element 102 of this figure. In order to avoidthat in convex regions of the optical processing element where twosurfaces form an angle of less than 180°, a rounded profile is producedinstead of a sharp linear boundary, a tool for forming this opticalprocessing element is separated into several pieces. Whenever the toolwould have a concave angle, the same is partitioned in order to ensuresharp edges of the optical processing element.

Still another embodiment of a prismatic optical processing element 102is shown in FIGS. 32 and 33. The problem of fabricating the prismaticstructure according to FIG. 31 or 32 (which essentially corresponds tothe one shown in FIG. 16) can be seen in the fact that the structure isthicker at one end than at the other. Such a difference in materialthickness impedes molding of the structure and for facilitating themolding process according to a further embodiment, the structure asshown in FIG. 33 can be used. Here, the base surface 146 opposing to theangled surfaces 144 is also angled with respect to the optical axis ofthe incident laser beam.

This modification does not have any impact on the generated radiationpattern, but facilitates the molding process due to an approximatelyconstant thickness of the optical processing element 102.

For an alignment with respect to the optical axis, either a respectiveangled surface at the main body 104 of the optical unit 100 can beprovided, or processing element 102 can be provided with projections atthe peripheral parts which provide a 90° bearing surface for beingsupported by the seating of the main body 104 of the optical unit 100.

Generally, an optical processing element 102 according to the presentinvention has the advantage that the minimum structural size of the toolis larger than of one single prism. This overcomes the problem thatsmall prismatic structures would be difficult to integrate into amolding tool. The edges at the transition from one prism to the nexthave to be very sharp in order to achieve a good contrast of theindividual spots. These sharp edges can be achieved according to thepresent invention by appropriately partitioning a molding tool.Furthermore, by combining different sizes of prisms, spots having adifferent brightness can be generated. According to the presentinvention, the different prisms are arranged so that some peaks of thetool are grouped together, wherein these groups can be built with onesingle part of the tool in order to keep the peaks sharp. The dimensionsof such a group are still much larger than only one single prism andthese groups are separated according to the peaks of the prismrepresenting indentations of the tool. Different brightness of the spotscan require very narrow prisms which may be fabricated in a reproducibleway with low tolerances by combining them with larger prisms.

Finally, it should be mentioned that the use of the terms “a” and “an”and “the” and similar referents in the context of describing theinvention (especially in the context of the following claims) are to beconstrued to cover both the singular and the plural, unless otherwiseindicated herein or clearly contradicted by context. The terms“comprising,” “having,” “including,” and “containing” are to beconstrued as open-ended terms (i.e., meaning “including, but not limitedto,”) unless otherwise noted. Recitation of ranges of values herein aremerely intended to serve as a shorthand method of referring individuallyto each separate value falling within the range, unless otherwiseindicated herein, and each separate value is incorporated into thespecification as if it were individually recited herein.

All methods described herein can be performed in any suitable orderunless otherwise indicated herein or otherwise clearly contradicted bycontext. The use of any and all examples, or exemplary language (e.g.,“such as”) provided herein, is intended merely to better illuminate theinvention and does not pose a limitation on the scope of the inventionunless otherwise claimed. No language in the specification should beconstrued as indicating any non-claimed element as essential to thepractice of the invention.

Exemplary embodiments are described herein. Variations of thoseembodiments may become apparent to those of ordinary skill in the artupon reading the foregoing description. The inventor(s) expect skilledartisans to employ such variations as appropriate, and the inventor(s)intend for the invention to be practiced otherwise than as specificallydescribed herein. Accordingly, this invention includes all modificationsand equivalents of the subject matter recited in the claims appendedhereto as permitted by applicable law. Moreover, any combination of theabove-described elements in all possible variations thereof isencompassed by the invention unless otherwise indicated herein orotherwise clearly contradicted by context.

Certain terminology is used herein for purposes of reference only, andthus is not intended to be limiting. For example, terms such as “upper,”“lower,” “above,” and “below” refer to directions in the drawings towhich reference is made. Terms such as “front,” “back,” “rear,”“bottom,” “side,” “left” and “right” describe the orientation ofportions of the component within a consistent but arbitrary frame ofreference which is made clear by reference to the text and theassociated drawings describing the component under discussion. Suchterminology may include the words specifically mentioned above,derivatives thereof, and words of similar import. Similarly, the terms“first,” “second” and other such numerical terms referring to structuresdo not imply a sequence or order unless clearly indicated by thecontext.

When introducing elements or features of the present disclosure and theexemplary embodiments, the articles “a,” “an,” “the” and “said” areintended to mean that there are one or more of such elements orfeatures. The terms “comprising,” “including” and “having” are intendedto be inclusive and mean that there may be additional elements orfeatures other than those specifically noted. It is further to beunderstood that the method steps, processes, and operations describedherein are not to be construed as necessarily requiring theirperformance in the particular order discussed or illustrated, unlessspecifically identified as an order of performance. It is also to beunderstood that additional or alternative steps may be employed.

It is specifically intended that the present invention not be limited tothe embodiments and illustrations contained herein and the claims shouldbe understood to include modified forms of those embodiments includingportions of the embodiments and combinations of elements of differentembodiments as coming within the scope of the following claims. All ofthe publications described herein including patents and non-patentpublications are hereby incorporated herein by reference in theirentireties.

What is claimed is:
 1. An optical unit for an alignment system of alight curtain monitoring a protective field, the optical unitcomprising: an optical processing element for generating a definedradiation pattern from a radiation emitted by an alignment radiationsource, and at least one additional optical functional element beingformed integrally with the optical processing element.
 2. The opticalunit of claim 1, wherein the optical functional element comprises a beamexpansion unit for adapting a cross sectional shape of a beam emitted bythe alignment radiation source to a dimension of an active area of theoptical processing element.
 3. The optical unit of claim 2, wherein thebeam expansion unit comprises a lens system according to at least one ofa Kepler or a Galileo beam expander configuration, a birefringentelement, and a cylindrical lens element.
 4. The optical unit of claim 1,wherein the optical unit comprises at least one of an optical wave guidefor guiding radiation from at least one display radiation source to asurface of the optical unit which is visible to an observer, and a lensfor focussing radiation forming the light curtain.
 5. The optical unitof claim 1, wherein the optical processing element is structured toform, in a planar observation region, a plurality of light pointsarranged in an essentially straight line from the radiation of a laserradiation source.
 6. The optical unit according to claim 5, wherein thelight points have different intensity, a central point or several pointshaving a higher intensity compared to a remaining points.
 7. The opticalunit according to claim 1, wherein the optical processing elementcomprises at least one of a micro-structured Diffractive Optical Element(DOE), an optical grating structure, and a prismatic structure.
 8. Theoptical unit according to claim 1, further comprising a mounting recessfor mounting the alignment radiation source, the mounting recess havingat least one alignment shoulder extending across a longitudinal axis ofthe recess for aligning the alignment radiation source with respect toits optical axis.
 9. The optical unit of claim 1, further comprising amounting recess for mounting the alignment radiation source, themounting recess having at least one alignment rib extending along alongitudinal axis of the recess for aligning the alignment radiationsource with respect to its optical axis.
 10. The optical unit of claim1, wherein the optical processing element comprises a prismaticstructure having a plurality of angled surfaces and a uniform basesurface opposite to these angled surfaces.
 11. The optical unit of claim10, wherein the base surface is oriented across an optical axis of anincident alignment radiation or includes angle different from 90° withthe optical axis.
 12. The optical unit of claim 1, wherein the opticalunit is fabricated as at least one of an integral molded part from aplastic material, or as a micromachined part from at least one of aglass, quartz, or plastic.
 13. The optical unit of claim 1, wherein aplurality of waveguide elements are formed at the optical unit, eachwaveguide being formed to image light from a status indicating LED ontoa display region of the optical unit.
 14. The optical unit of claim 1,wherein a plurality of lenses are formed at the optical unit, each lensbeing formed to focus radiation transmitted to cover the protectivefield.
 15. An alignment system for a light curtain monitoring aprotective field, the light curtain comprising a first support elementand a second support element, wherein the protective field is covered byradiation transmitted between the support elements, wherein thealignment system comprises at least one alignment radiation source beingarranged on the first support element and at least one alignmentradiation receiver arranged on the second support element for receivingthe alignment radiation and for providing an alignment signal indicatinga correct positioning of the two support elements with respect to eachother, the alignment system further comprising at least one optical unithaving an optical processing element for generating a defined patternfrom the radiation emitted by the at least one alignment radiationsource.
 16. The alignment system according to claim 15, furthercomprising at least one additional optical functional element beingformed integrally with the optical processing element.
 17. The alignmentsystem according to claim 15, wherein the alignment radiation receivercomprises a target surface for reflecting the radiation pattern, thereflection forming the alignment signal.
 18. A light curtain formonitoring a protective field, the light curtain comprising a firstsupport element and a second support element, wherein the protectivefield is covered by radiation transmitted between the support elements,and an alignment system for the light curtain, the light curtaincomprising a first support element and a second support element, whereinthe protective field is covered by radiation transmitted between thesupport elements, wherein the alignment system comprises at least onealignment radiation source being arranged on the first support elementand at least one alignment radiation receiver arranged on the secondsupport element for receiving the alignment radiation and for providingan alignment signal indicating a correct positioning of the two supportelements with respect to each other, the alignment system furthercomprising at least one optical unit having an optical processingelement for generating a defined pattern from the radiation emitted bythe alignment radiation source.
 19. A light curtain according to claim18, wherein the first support element and the second support elementeach comprise: a plurality of light emitting elements and lightreceiving elements, wherein the light emitting elements and lightreceiving elements are operable to form a light grid from a plurality oflight barriers formed between opposing light emitting elements and lightreceiving elements, a control unit for processing output signalsgenerated by the light receiving element and for generating a definedoutput signal upon interruption of at least one light barrier, at leastone alignment radiation source with the optical processing element, atleast one alignment radiation detector element for detecting thealignment radiation processed by the optical processing element.
 20. Thelight curtain according to claim 18, wherein each support elementcomprises: a transceiver unit carrying a plurality of light emittingelements and light receiving elements, an alignment radiation source andan optical unit, and at least one separate detachable plug-in module,wherein the first and second transceiver units are identically built,whereas the first and second plug-in modules differ from each other andthus define a functionality of the respective support element.